Mr Sanford, 59, is expected to centre his campaign on cutting government debt and spending.

"I think we need to have a conversation on what it means to be a Republican. I think that as a Republican party we have lost our way," he told Fox News on Sunday.

"We have lost our way on debts and deficits and spending... The president has called himself the king of debt, has a familiarity and comfort level with debt that I think is ultimately leading us in the wrong direction."

Who is Mark Sanford?

He first served in Congress in 1995, representing South Carolina's first congressional district. He later served as the state's governor for two terms from 2003-2011. He then returned to the House in 2013.

Mr Sanford criticised Mr Trump during the 2016 presidential election but ultimately supported him. However he would become one of his toughest Republican critics in Congress when Mr Trump took office.

That stance cost him the Republican primary when his seat was up for re-election last year. He was beaten by a pro-Trump challenger who went on to lose the election to her Democrat opponent.

He is known as a fiscal conservative and has been attacked by Mr Trump over an extra-marital affair that tainted his second term as governor.